The present invention concerns hydraulic control of motor vehicle clutches and in particular hydraulic vibration absorbers included therein.
A control system of the above kind is described in document FR-A-2 442 156.
In the above application the control device 1 (FIG. 1) includes a clutch pedal 2, a hydraulic sender 3 forming a master cylinder and a receiver 5.
In a manner that is known in itself the sender 3 includes a fixed cylinder in which a piston connected by a rod 31 to the clutch pedal 2 moves axially.
Here the upper part of the pedal is hinged at 20 to a fixed part of the vehicle.
A hydraulic pipe 4 connects the master cylinder 3 to the receiver 5 forming the cylinder actuating the clutch 29 of the motor vehicle, which includes a diaphragm 37, a cover 33, a pressure plate 38, a disc 41 and a reaction plate 30. The control fluid passes through this pipe. The receiver 5 is a mirror image of the sender and includes a fixed cylinder within which a piston connected by a rod 51 to a clutch release fork 6 moves axially, the fork acting in a manner that is known in itself on a clutch release thrust bearing 36 of the clutch 29 in contact with a diaphragm 37 in bearing engagement with a cover 33 to act on a pressure plate 38 in order to clamp the friction linings of a friction disc 41 between the pressure plate 38 and the reaction plate 30 of the clutch 29, forming a drive flywheel.
The cover is fixed to the reaction plate which is constrained to rotate with the crankshaft of the engine of the vehicle and the friction disc is constrained to rotate with the input shaft of the gearbox.
The receiver 5 therefore acts directly or indirectly on the clutch release abutment of the clutch 29 to operate said clutch driven by the engine of the vehicle.
For more information see document FR-A-2 730 532.
In the above document the receiver can include a piston acting directly on the clutch release thrust bearing, the receiver being of the concentric type and the input shaft of the gearbox passing through it.
In all cases the piston and the cylinder define a variable volume chamber.
When the clutch is released the sender is pressurised by the pedal 2 when it is depressed by the driver, the volume of the control chamber of the sender 3 is reduced and the volume of the control chamber of the receiver 5 is increased. The opposite happens when the clutch is engaged, the volume of the control chamber of the receiver decreasing and the volume of the control chamber of the sender increasing, said chamber then being depressurised.
Thus control fluid is transferred from one chamber to the other.
To release the clutch the driver presses the clutch pedal and vibration from the engine is transmitted to said pedal via the clutch release thrust bearing 36, the receiver 5, the pipe 4 and the sender 3.
This vibration is uncomfortable for the driver and varies with the rotation speed of the engine. It is particularly intense in vehicles with a diesel engine. The effect is amplified by the geometrical imperfections of the diaphragm 37, not all fingers of which are in the same plane because the diaphragm is frustoconical in the relaxed condition and undergoes heat treatment.
For this reason a hydraulic vibration absorber 10 is provided in the pipe 4. The hydraulic absorber 10 is fixed to a fixed part of the vehicle and absorbs fluctuations in hydraulic pressure coming from the receiver 5 and caused by vibration of the engine of the vehicle to prevent said fluctuations propagating to the sender 3 and therefore to the pedal 2.
To this end the pipe 4 is in two parts 4a and 4b respectively connected to the sender 3 and the vibration absorber 10 and to the receiver 5 and the vibration absorber 10.
The vibration absorber 10 has a hollow body with respective orifices connected to the parts 4a and 4b, for example in the form of pipes. The absorber 10 also includes, between the above two orifices, a cavity in which a piston reciprocates to compress and allow to expand a block of elastic material disposed outside it so as not to come into contact with the control fluid.
To this end the shouldered piston carries a seal and the elastic material block bears on the exterior of the body of the hydraulic absorber.
The above solution therefore requires a large number of components. Also, it is bulky in the heightwise (vertical) direction.
An aim of the present invention is to provide a simple and economic way to overcome the above drawbacks.
In accordance with the invention a vibration absorber of the type indicated above is characterised in that an elastic material block is mounted in a housing of the body of the vibration absorber and in that the cavity, forming a fluid chamber, is delimited by the elastic material block sealingly closing the cavity and bearing on an abutment fastened to the body of the vibration absorber.
The invention reduces the number of components because the elastic material block has a sealing function and a vibration absorbing function.
The heightwise overall size is also reduced and there is no piston that is bulky in the radial direction. The vibration absorber is therefore compact and economic.
In accordance with one feature of the invention the housing is shouldered for bearing engagement with a first pierced disc disposed between said cavity and the elastic material block. Because of the first disc the block is subjected to the action of the control fluid and can therefore absorb vibration directly. The damper is controlled by the holes in the first disc in conjunction with the stiffness of the elastic material block. The shouldered housing communicates with the cavity.
The first disc can therefore bear on the shoulder and to provide the seal the elastic material block is in intimate contact with at least a portion of the outside periphery of the housing, i.e. with a portion of the lateral face(s) of the housing.
Assembly is therefore simple and is effected by threading the components onto each other.
The abutment advantageously comprises a second disc with holes in it. The elastic material block has at least one recess facing a hole in the second disc to assure circulation of air and to control the deformation of the block. The block can be hat-shaped so that it deforms laterally (horizontally).
The second disc is held in place by a U-shaped pin the branches of which are engaged in passages provided for this purpose in the body of the absorber.
A different variant can use different means, for example an externally screwthreaded washer engaged with a screwthread in the internal bore of the housing.
In a further embodiment the second disc is glued, welded, crimped or clipped to the body of the absorber or fixed by a circlip.
The block between the first disc and the abutment can be pre-stressed. In all cases the hydraulic absorber forms an assembly that can be handled and transported and tested prior to installation.
The damper can be attached to the receiver or to the sender, in which case the pipe is in one part.
The damper does not need to be fixed to a fixed part of the vehicle. The first disc can be dispensed with.